<p>While <code>null</code> is technically a valid <code>Boolean</code> value, that fact, and the distinction between <code>Boolean</code> and
<code>boolean</code> is easy to forget. So returning <code>null</code> from a <code>Boolean</code> method is likely to cause problems with callers'
code.</p>
<h2>Noncompliant Code Example</h2>
<pre>
public Boolean isUsable() {
  // ...
  return null;  // Noncompliant
}
</pre>
<h2>See</h2>
<ul>
  <li> <a href="http://cwe.mitre.org/data/definitions/476.html">MITRE CWE-476</a> - NULL Pointer Dereference </li>
  <li> <a href="https://wiki.sei.cmu.edu/confluence/x/aDdGBQ">CERT, EXP01-J.</a> - Do not use a null in a case where an object is required </li>
</ul>

